This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-304943 filed on Oct. 4, 2000, and 2001-231690 filed on Jul. 31, 2001.
1. Field of the Invention
The present invention relates to a method for manufacturing a valve timing adjusting apparatus for changing a valve timing of an internal combustion engine.
2. Description of Related Art
In a conventional vane type valve timing adjusting apparatus, a vane member rotating together with a camshaft is housed relatively rotatably within a housing member receiving a drive force from a crank-shaft of the engine. A phase of the vane member with respect to the housing member, that is, a phase difference caused by the relative rotation of the crank-shaft and the camshaft is hydraulically controlled, thereby adjusting the valve timing of at least one of an intake valve and an exhaust valve.
The housing member and the vane member are manufactured by cutting an article obtained by sintering iron, or an article obtained by molding aluminum by way of die-casting or forging.
Torque for relatively rotating and driving the housing member and the vane member by the fluid pressure differs in accordance with an engine size. The torque can be set by adjusting the volume of a fluid chamber.
However, in the molding by way of sintering, die-casting or forging, it is necessary to prepare different molds for changing the volume of the fluid chamber, and perform molding for every mold. Thus, in the production by way of sintering, die-casting or forging, the cost of manufacturing molds increases due to the increase of the number of molds. Further, the arranging steps for preparing different molds for every different torque are increased.
Portions removed of a molded body molded by die-casting or forging are shown in FIGS. 16 and 17. The cross-hatching area shows the portion to be removed.
FIGS. 15A and 15B show a removed portion which is removed when a housing member and a vane member are made by die-cast molding. Gate residues 301, 311, squeeze residues 302, 312, and pattern-draw slope portions 303, 313 are removed from a die-cast molded body 300 of a housing member and a die-cast molded body 310 of a vane member.
FIGS. 16A and 16B shows a portion which is removed when a housing member is made by forging. A surface portion 321 on the forging side, an inner wall portion 322 of a peripheral wall and a side wall, and a through-hole portion 323 are removed from a forge-molded body 320 of the housing member.
FIGS. 17A and 17B show a portion which is removed when a vane member is made by forging. A bottom portion 331 of forging and a surface portion 332 of forging are removed from a forge-molded body 330 of a vane member.
As described above, in the die-cast molding, there are many portions removed by cutting such as gate part, squeeze residues and pattern-draw slopes. In the forge-molding, there are many portions removed by cutting after forging. Accordingly, materials are wasteful, and the number of manufacturing processes increases.
Conventionally, in a case where one of side walls and the peripheral wall of the housing member are integrally modled by die-casing, and the vane member is made of die-casting material, an aluminum material containing 7-12% of Si is used due to the readiness of die-casting. When the aluminum material containing 7-12% of Si is used, the agglutination between aluminums might occur in the sliding portion between the inner surface of the side wall of the housing member and the side surface of a vane rotor. It is necessary to apply Sn plating on the sliding spot and to apply the surface treatment such as coating of alumite or fluorine resin for preventing the agglutination of the sliding part.
An object of the present invention is to provide a method for manufacturing a valve timing adjusting apparatus in which the number of manufacturing steps is reduced and the drive torque by way of the working fluid is easily adjusted.
According to the present invention, light metal is used, and an extruded molded article is cut into the desired length to form a molded article of at least one of the peripheral wall of a housing and a vane member. Therefore, a member different in the length of a rotational shaft can be manufactured by the same extrusion mold. By adjusting the length of the rotational shaft, the volume of a housing chamber is set to change the torque of the working fluid for relatively rotating and driving the vane member with respect to the housing member. Accordingly, in a case where a valve timing adjusting apparatus according to the different torque is manufactured, the number of steps for the manufacture of molds can be reduced. Preferably, light metal used as an extrusion material is an alloy of aluminum, magnesium or copper.
Further, since the cutting process amount after molding can be reduced as compared with molding by way of forging and die-casting, wastefulness of material and the number of manufacturing steps are reduced.